Vannette Lab: Diverse Plants Protect Their Nectar with Varying Levels of Hydrogen Peroxide
Leta Landucci Heads Research Project
Humans use the chemical compound, hydrogen peroxide, as a disinfectant, bleach, and antiseptic, but a newly published UC Davis study indicates that “diverse plant species, not just tobacco, protect their nectar from bacteria and fungi by producing varying levels of hydrogen peroxide.”
“This is an example of how plants preserve their sugar nectar—a reward for their pollinators—from microbial spoilage,” said community ecologist Rachel Vannette, associate professor and vice chair of the UC Davis Department of Entomology and Nematology.
The research, led by post-baccalaureate research fellow Leta Landucci of the Vannette lab, appears in the current issue of New Phytologist, an international, peer-reviewed journal dedicated to plant science research and its applications.
The UC Davis study, "Nectar Peroxide: Assessing Variation Among Plant Species, Microbial Tolerance, and Effects on Microbial Community Assembly," originated when Landucci read scientific literature about how tobacco plants defend their nectar against microbes. “I was intrigued to read that tobacco plants are known to defend their nectar against microbes by producing hydrogen peroxide through a series of specialized enzymes called nectarins,” said Landucci, now a graduate student at the University of Minnesota, Twin Cities. “I wondered about the ecological and evolutionary context of this peroxide production.”
Curious how the production of hydrogen peroxides secreted within floral nectar influences microbial growth and how it may function as a defensive compound to protect against pathogenic infection, Landucci sampled nectar from many different plant species to see if other species also produce peroxide; if peroxide was inducible by plant hormones; and how it affects microbial growth.
Her research drew financial support from a National Science Foundation-Post-Baccalaureate Students (NSF-REPS) grant, a supplement to Vannette’s NSF Career (Faculty Early Career Development Program) award. “The NSF-REPs funding enabled research opportunities for students whose science education was impacted by COVID,” Vannette noted.
Landucci and Vannette looked at the impact of plant-produced hydrogen peroxide on microbial growth in floral nectar. They first conducted a widespread survey of floral nectar extracted from plants on the UC Davis campus, the UC Davis Arboretum and Public Garden, the Sierra mountain range, and surveyed the literature for previously studied species.
"We surveyed 45 flowering plant species distributed across 23 families and reviewed the literature for measurements of 13 other species to assess the field-realistic range of nectar hydrogen peroxide (Aim 1) and explored whether plant defense hormones induce nectar hydrogen peroxide upregulation (Aim 2)," they wrote in their abstract. "Further, we tested the hypotheses that variation in microbial tolerance to peroxide is predicted by microbe isolation environment (Aim 3), that increasing hydrogen peroxide in flowers alters microbial abundance and community assembly (Aim 4), and that microbial community context affects microbial tolerance to peroxide (Aim 5)."
“We found that nectar peroxide is commonly produced in many plant species, but highly variable, ranging from undetectable to up to 3000 micro molar concentration, with 50 percent of species containing less than 100 micro molar,” Vannette said. “This was interesting because it pointed to the need to study the impact of lower concentrations of peroxide on microbes than had previously been investigated.”
“We used a combination of field studies and lab experiments,” Vannette said. “First, in the lab we looked at how a field realistic range of hydrogen peroxide differentially impacted the growth of microbes--both fungi and bacteria--from various sources such as from pollinators, flower tissue, and nectar. Next, we ran a field experiment using California fuschia (Epilobium), growing on the UC Davis campus, and enzymatically increased the concentration of hydrogen peroxide in the flower nectar.”
They then added a community of five common nectar bacteria, and after a day’s time, looked at how the microbial community composition changed in the presence of increased hydrogen peroxide.
“For the last lab experiment, we tested whether microbes could detoxify hydrogen peroxide, and whether microbes growing together versus alone alter microbial tolerance to high hydrogen peroxide conditions,” Vannette shared. “Together, our results suggest field realistic ranges of hydrogen peroxide are not as pervasive and antimicrobial as we anticipated, though this could be because many of the microbes we used are likely adapted to nectar and pollinator-associated environments, which are commonly enriched in peroxide.”
“Even so, our findings still suggest that the microbes we tested do indeed vary in their tolerance to hydrogen peroxide, and also have different detoxification abilities. Further, we found that microbes grown in community seem to facilitate the survival and growth of less peroxide-tolerant species, which provides insights into the importance of community dynamics in microbial colonization of nectar.”
Vannette, a Chancellor’s Fellow and an international leader in microbial ecology, studies interactions between plants, insects and microbes. She focuses on the chemical and microbial ecology of plant-pollinator interactions and how microbes influence plant defense and resistance against insect pests.
Landucci, who received a bachelor of science degree in biochemistry, with honors, in 2022 from the University of Wisconsin-Madison, served as an undergraduate research assistant at UW and at the Great Lakes Bioenergy Research Center, Madison, and is an alumna of Young Voices of Science, Hubbard Brook Research Foundation. She accepted a full-time post-baccalaureate research fellow position at UC Davis in September 2022. She joined the lab of Professor Emilie Snell-Rood at the University of Minnesota in 2024.
The New Phytologist is owned by the New Phytologist Foundation, a not-for-profit organization dedicated to the promotion of plant science. Research falls into five sections: Physiology and Development, Environment, Interaction, Evolution, and Transformative Plant Biotechnology. Covering all aspects of botany, it was established in 1902 by Arthur Tansley, who served as the editor until 1931.